Preconditioning of alumina-supported platinum hydroforming catalysts



United States Patent Ofiice 2,876,195 Patented Mar. 3, 1959 PRECONDITIONING OF ALUMINA-SUPPORTED A PLATINUM HYDROFORMING CATALYSTS Russell V. Malo, Munster, and Kenyon A. Hyle, Ross Township, Lake County, Ind., assignors to Standard Oll Company, Chicago, 11]., a corporation of Indiana No Drawing. Application November 29, 1954 Serial No. 471,905

6 Claims. (Cl. 208-438) This invention relates to the reforming of hydrocarbons. More particularly, it relates to the hydroforming of petroleum naphthas in the presence of an aluminaproved processes for upgrading petroleum napthas. One

of the more successful of the new techniques employs platinum-alumina catalysts for reforming naphthas at elevated temperature and pressure in the presence of added hydrogen. The new development is capable of producing gasolines of high octane number and desirable volatility characteristics in excellent yield over a long period of time, when employed with precautions to avoid poisoning of the catalytic metal by various trace components in the charging stocks. Ordinarily, however, platinumalumina catalysts tend to undergo a more or less steady decline in activity, as evidenced by the octane number of the product, depending upon a number of the operating variables, primarily the temperature, pressure, charging stock end-point, the concentrations of deleterious substances such as sulfur, arsenic, nitrogen, and the like in the charging stock, and the relativeproportions of such substances. Moreover, all of the various deleterious effects tend to be emphasized at the high treating temperatures which are normally required to obtain premium gasolines having an F-1 clear octane number of 90 or higher, making it correspondingly difficult to produce a reformate pool having an average octane number of the desired level. To'minimize this problem, we have now discovered a technique of operation whereby the octane-number decline rate for platinum-alumina catalysts during the reforming of petroleum naphthas can be substantially reduced. It is therefore an object of our invention to improve the reforming of hydrocarbons, in particular the hydroforming of petroleum naphthas. in the presence of alumina-supported platinum catalysts. Another object is to increase the reformate pool octane number obtainable with platinum-alumina catalysts. further object is to extend the effective life of platinumalumina hydroforming catalysts. These and other objv-CtS of our invention will be apparent from the appended description and claims.

Our invention is basically a method for preconditioning a platinum-alumina catalyst to render it less susceptible to the action of catalyst poisons and/or inhibitors existing in hydroformer charging stocks. 'In our new process, a platinum-alumina catalyst is subjected to a preliminary contact under coke-forming conditions with a hydrocarbon stock substantially free from deleterious substances. After the catalyst has been pretreated in this way, it is capable of hydroforming a petroleum naphtha containing substantial quantities of normally deleterious substances while maintaining its catalytic properties over an extended period of operation.

Our new technique is broadly applicable in the treatment of inhibited or poison-containing petroleum naph- 2 thus to produce gasoline products having clear F-l octane numbers of 90 to 100 or higher, for example, 95 to 105. The hydroforming process is ordinarily, carried out at a pressure within the range of about 100 to 1,000 pounds per square inch gage, atemperature between about 850 and 1000 R, an hourly weight space velocity between about 0.5 and 5, and a hydrogen input rate between about 2,000 and 10,000 standard cubic feet per barrel of charging stock. For a product octane level above about 95, the pressure should preferably be between about 100 and 500 pounds per square inch gage, the temperature betweenabout 925 and 975 F., and the space velocity between about 0.5 and 2. Under the foregoing conditions, it is commonly observed that the catalyst declines in activity at a rate greater than 2 F-l octane numbers per 100 hours if the charging stock contains more than about 0.1 weight-percent of sulfur, more than about parts per million of nitrogen, more than about 10 parts per million of arsenic, selenium, or tellurium, or minor proportions within the same general range of other substances known to be deleterious to platinum. Among such stocks are coke-still naphthas, West Texas virgin naphtha, West Coastnaphthas, Kuwait naphthas, and the like. Many of thesestocks contain a multiplicity of injurious substances, l r vexample both sulfur and nitrogen. 1; i

In conditioning a-p atinu'm-alumina catalyst for con tact with such charging 'stocks, we subject the catalyst to a preliminary treatment with a Mid-Continent virgin naphtha, or other low-sulfur, low-nitrogen, substantially poison-free petroleum fraction under conditions of temperature, pressure, and contact time to deposit a layer of carbon thereon, suitably between about on-and 10 percent by weight of carbon based on the to l catalyst weight. Virtually any hydrocarbon stock o pure, hydrocarbon is satisfactory for this purpose,."'p'rovided only that it is substantially free from deleterioussubstances and can be induced to disproportionate and deposit a protective layer of carbon on the catalyst under the treating conditions employed. Satisfactory stocks include Mid-Continent virgin naphtha, hydroformed naphthas, hydrofined naphthas, sweet straight-run gasolines and certain other stocks such as gas oils and cracked cycle oils having the characteristics noted above. Also suitable are heptanes, heptenes, octanes, octenes, nonanes, no-

nenes, cyclopentane, cyclopentene, cyclohexene, methylcyclohexene, or the like, either alone or in admixture, or dissolved in a more refractory naphthenic or aromatic hydrocarbon. A dilute solution of cyclopentadiene (e. g., 1 to 10 volume-percent) or other polyolefin in benzene or other aromatic hydrocarbon liquid is an especially rapid and effective coke former. The pretreatment is satisfactorily carried out at a temperature between about 850 and 950 F, a pressure below about 500 pounds per square inch gage, and a weight hourly space velocity within the usual hydroforming range of about 0.5 to 5 for a period of around 5 hours or more, sufiicient to deposit at least about 0.1 percent by weight of carbon on the catalyst. We prefer to carry out the pretreatment for a sufiicientlength of time to deposit between about 0.1 and 2 percent by weight of carbon on the catalyst, operating under thehydroforming conditions thereafter to be employed, with the exception that the temperature is maintained from 10 to 50 F. below .the projected hydroforming temperature. For this purpose, a pretreating time of around 1 to hours is ordinarily sufficient, depending upon the refractoriness of the stock employed in the pretreatment. I

By the foregoing means, we have succeeded in effecting a large decrease in the activity decline rates of platinumalumin'a catalysts when employed for the hydroforming of I 3. low-quality charging stocks. After catalysts have been treated in this way, we find that they commonly decline in activity in the ensuing hydroforming operation at a rate less than half the rate ordinarily observed, sometimes at a rate of 2 F-l octane numbers per 100 hours or lower. The extent ofimprovement in each case depends upon the degree of pretreatment and upon the severity of charging-stock contamination.

'lhe etfectiveness of our new technique is conveniently illustrated in connection with the hydroforming of a West Texas naphtha containing sulfur compounds equivalent to 0.3 percent by weight of sulfur. When such a naphtha is hydroformed over a 0.6 percent platinum-om alumina catalyst at a temperature of 940 F., a pressure of 200 pounds per square inch gage, an hourly weight space velocity of 2, and a hydrogen rate of 5,000 standard cubic feet per barrel of feed, a gasoline reformate is obtained initially having an F-l rating of 99 to 100, but declining at the rate of around 20 octane numbers per 100 hours on stream. When the catalyst is subjected to a preliminary treatment for l to hours under the same conditions with a Mid-Continent virgin naphtha containing 0.03 percent sulfur, the activity decline rate in the subsequent hydroforming of the West Texas naphtha isreduced to less than 10 octane numbers per 100 hours onstream.

We are uncertain as to the precise mechanism whereby the advantageous results of our preconditioning operation are achieved. Our technique is not; an equivalent of rerunning, acid treating, clay treating, silica-gel treating, or any of the other methods commonly employed for removing contaminants from petroleum stocks, since such methods do 'not produce the improved catalyst activity maintenance typical of our invention. It is possible that thelayer of carbon deposited by our pretreatment step acts as a protective shield for the catalyst, preventing access of poisonous materials to the active metallic centers. It is alsopossible that the pretreatment step conditions the catalytic metal against adsorption of non-carbonaceous materials, and thereby prevents effective contact of poisonous materials with the active catalytic centers. These possibilities, however, are advanced only as reasonable hypotheses, and it is to be understood that we do not wish to bebound thereby. our pretreating step is effective in prolonging the useful cycle life of platinum-alumina catalysts.

Our invention will be more fully understood from the following operating example:

Example A West=Texas naphtha having an ASTM boiling range of 250 to 420 F. and containing 38 percent saturated an hourly weight space velocity of 2, and a hydrogen addition rate of 5,000 standard cubic feet per barrel. The product was .collected over -hour intervals and tested, with the following results:

Product interval, hrs.: Product octane number (F-l) 0-20 99.0

It will be observed that the catalyst activity was initially high, but the activity decline rate was also high, approaching 18 octane units per 100 hours on stream.

In a comparative test, the catalyst was subjected to pretreatment for 2 hours under the defined hydroforming conditions with a Mid-Continent virgin naphtha having an Whatever its method of action,v

ASTM boiling range of 199 to 350 F. and containing 52 percent paraflins, 0.5 percent olefins, percent naphthenes, and 8 percent aromatics, by volume, together with 0.03 percent sulfur. At the end of this timc, the Mid- Continent naphtha feed was discontinued and the introduction of the West Texas naphtha, described above, was

begun. The results were as follows:

Product interval, hrs.: Product octane number (F-l) 2-20 99.3 2o-4ov 98.3 40-60 96.8 60450 94.3 -100 91.1

The above data correspond to an activity decline rate of 7.6 F-l octane units per hours, a marked improvement over the activity maintenance obtained with an untreated catalyst.

Our new process is effective for preconditioning alumina-supported platinum hydroforming catalysts in general, many types of which have been described in the prior art. It can be used, for example, in connection with unpromoted. platinum-on-alumina, or with platinumalumina catalysts which include a promoting additive such as vanadia, chromia, titania, iridium, an oxide of phos phorus, or the like, or a mild cracking adjuvant, such as boria, silica, fluorine, chlorine, or the like. The catalysts commonly contain platinum in a proportion between about 0.05 and 1 percent by weight, based on dry Al,0,. Promoters and other additives are usually employed in a proportion between about 0.1 and 8 percent by weight.

While we have described our invention with reference to certain specific embodiments thereof, it is to be understood that such embodiments are illustrative only and not by way of limitation; Numerous alternative charging stocks, catalysts, manipulative steps, and operation con- 'ditions will be apparent from the above description to those skilled in the art.

In accordance with the foregoing description, we claim as our invention:

1. Ina method' for hydroforming a petroleum naphtha in the presence of an alumina-supported platinum catalpt v under conditions adapted to produce therefrom a gasoline having an F-l octane number above about 90, said petroleum naphtha containing substances ordinarily deleterious to said catalyst whereby the activity of said catalyst in said hydroforming operation ordinarily becomes impaired, and said conditions being a temperature between about 850 and 1000' F., a pressure below about 500 pounds per square inch gage, and a weight hourly space velocity between about 0.5 and 5, the improvement which comprises preconditioning said catalyst prior to said hydroforming operation by exposing said catalyst when fully active to contact under said conditions with a hydrocarbon stock substantially free from such deleterious substances for a period of time sutlicient to deposit between about 0.1 and 10 percent of coke thereon,

wherebythe activity maintenance of said catalyst in the ensuing hydroforming operation is substantially improved.

2. In a method for hydroforming a petroleum naphtha in the presence of an alumina-supported platinum catalyst under conditions adapted to'produce therefrom a gasoline having an F-l octane number above about 90, said petroleum naphtha containing substances ordinarily deleterious to said catalyst whereby the activity of said catalyst in said hydroforming operation ordinarily declines at a rate greater than 2 F-l' units per 100 hours, and said conditions'beinga temperature between about 850 and 1000" E, a pressure below about 500 pounds per square inch gage, and a weight hourly space velocity between about 0.5 and 5, the improvement which comprises preconditioning said catalyst prior 'to said hydro- I forming operation by exposing said jcatalyst when fully active to contact under said conditions with a petroleum Phi t llbstantially free from such [deleterious sub 1 stances for a period of time sufficient to deposit between about 0.1 and percent of. coke thereon, whereby the rate of decline in activity of said catalyst in the ensuing a pressure below about 500 pounds per square inch gage,

and a weight hourly space velocity between about 0.5 to 5, and obtaining therefrom a gasoline having an F1 octane number above about 90, in which operation the activity of said catalyst ordinarily declines at a rate greater than 2 F-l units per 100 hours, the improvement which comprises preconditioning said catalyst prior to said hydroforming operation by exposing said catalyst when fully active to contact under said conditions with a pctroleum naphtha substantially free from sulfur and other substances deleterious to said catalyst for a period of time sufficient to deposit between about 0.1 and 2 percent by weight of coke on the said catalyst, whereby the rate of decline in activity of the said catalyst in the ensuing hydroforming operation is reduced to less than half the rate of decline observed in the absence of the said preconditioning.

4. In a method for hydrot'orming a petroleum naphtha in the presence of an aluminasupported platinum catalyst at hydroforming conditions, said conditions being a temperature between about 850 and 1000 F., a pressure below about 500 pounds per square inch' gage, and a weight hourly space velocity between about 0.5 to 5, and obtaining therefrom a gasoline having an F--l octane number above about-90, said petroleum naphtha containing a nitrogen compound ordinarily deleterious to said catalyst, the improvement which comprises preconditioning said catalyst prior to said hydroforming operation by exposing said catalyst when fully active to contact under said conditions with a petroleum naphtha substantially free from said nitrogencontaining compound and other substances ordinarily deleterious to said catalyst for a period of time sufficient to deposit between about 0.1 and 2 percent by weight of carbon on the said catalyst, whereby the rate of decline in activity of said catalyst in the ensuing hydroforming operation is reduced to less than half the rate of decline observed in the absence of the said preconditioning.

5. In a method for hydrot'orming a petroleum naphtha in the presence of an alumina-supported platinum catalyst at hydroforming conditions, said conditions being a temperature between about 850 and 1000 F., a pressure between about 100 and 500 pounds per square inch gage, and a weight hourly space velocity between about 0.5 and 5, and obtaining therefrom a gasoline having an F-l octanenumber above about 90, said petroleum naphtha containing substances ordinarily deleterious to the activity of the said catalyst, the improvement which comprises preconditioning said catalyst prior to said hydroforming operation by exposing said catalyst when .fully' active to contact at said conditions with a pure hydrocarbon for a period, between about 0.1 to 100 hours, suflicient to disproportionate said pure hydrocarbon and to deposit between about 0.1 and 10 percent by weight of carbon on said catalyst, whereby the activity maintenance of the said catalyst in the ensuing hydroforming operation is substantially improved.

6. In amethod for hydroforming a petroleum naphtha in the-presence of afixed-bed catalyst consisting essentially of alumina and between about 0.05 and 1 percent by weight of platinum,- based on dry A1 0 at hydro forming conditions, said hydroforming conditions being a pressure between about 100 and 500 pounds per square inch gage, a hydroforming temperature between about 850 and 1000 F., and a weight hourly space velocity between about 0.5 and 5, sufficient to obtain therefrom a gasoline .having an F-l octane number between about and 105, said petroleum naphtha containing sulfur and nitrogen compounds ordinarily deleterious to the activity of said catalyst, whereby the activity of said catalyst ordinarily declines at a rate greater than 2 E4 octane units per hours, the improvement which comprises preconditioning said'catalyst prior to said hydroforming operation by exposing said catalyst when fully active for a period of between about 1 and 100 hours to contact under said hydroforming conditions with a hydroformate obtained from said petroleum naphtha, said hydroformate being substantially free from said deleterious substances, whereby between about 0.1 and 2 percent by weight of coke is deposited on said catalyst and the rate of declinein activity of said catalyst in the ensuing hydroforming operation is reduced to less than half the rate of decline observed in the absence of the said preconditioning.

Mme. Cited in the tile of this patent UNITED STATES PATENTS 2,689,208 Murray et al. -..L. Sept. 14, 1954 2,723,946 Donaldson Nov. 15, 1955 

1. IN A METHOD FOR HYDROFORMING A PETROLEUM NAPHTHA IN THE PRESENCE OF AN ALUMINA-SUPPORTED PLATINUM CATALYST UNDER CONDITIONS ADAPTED TO PRODUCE THEREFROM A GASOLINE HAVING AN F-1 OCTANE NUMBER ABOVE ABOUT 90, SAID PETROLEUM NAPHTHA CONTAINING SUBSTANCES ORDINARLY DELETERIOUS TO SAID CATALYST WHEREBY THE ACTIVITY OF SAID CATALYST IN SAID HYDROFORMING OPERATION ORDINARILY BECOMES IMPAIRED, AND SAID CONDITIONS BEING A TEMPERATURE BETWEEN ABOUT 850 AND 1000*F., A PRESSURE BELOW ABOUT 500 POUNDS PER SQUARE INCH GAGE, AND A WEIGHT HOURLY SPACE VELOCITY BETWEEN ABOUT 0.5 AND 5, THE IMPROVEMENT WHICH COMPRISES PRECONDITIONING SAID CATALYST PRIOR TO SAID HYDROFORMING OPERATION BY EXPOSING SAID CATALYST WHEN FULLY ACTIVE TO CONTACT UNDER SAID CONDITIONS WITH A HYDROCARBON STOCK SUBSTANTIALLY FREE FROM SUCH DELETERIOUS SUBSTANCES FOR A PERIOD OF TIME SUFFICIENT TO DEPOSIT BETWEEN ABOUT 0.1 AND 10 PERCENT OF COKE THEREON, WHEREBY THE ACTIVITY MAINTENANCE OF SAID CATALYST IN THE ENSUING HYDROFORMING OPERATION IS SUBSTANTIALLY IMPROVED. 